(ITS#3836) slapd-monitor man page update

Full_Name: Quanah Gibson-Mount
Version: 2.2.27
OS: Solaris 8
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (171.64.19.82)
The man page for back-monitor fails to mention that the attributes storing data
in back-monitor are operational, leading to unnecessary confusion from users who
don't see any data after enabling the monitor backend. Documenting this in the
man page would help end users.